Examples of known documents disclosing factors having an effect on the particle size distribution and specific process for controlling the particle size distribution include Japanese Patent Publication No. 13232/1979. In this publication, there is a description to the effect that introduction of a dehydrated waste gas in a reaction chamber makes the particle size small and, at the same time, makes the particle size distribution narrow.
Examples of known documents with respect to the control of the aggregate size distribution include Japanese Patent Application Laid Open Nos. 42773/1982 and 223865/1985 which disclose that the aggregate size distribution is controlled by axially spraying a raw material into a combustion gas filling chamber to mix it with a combustion gas and then changing the flow state of the mixture within a furnace through a throat portion and an expanding portion.
Japanese Patent Publication No. 1005/1972 is a known document on the injection of a thermally decomposable material hydrocarbon into a combustion gas at a high temperature wherein a material hydrocarbon is directly injected into a high-speed flow of a combustion gas. Specifically, in this apparatus, a material hydrocarbon is injected into a throat portion of a combustion chamber and the portion provided directly after the throat portion constitutes a reaction zone. The reaction zone is provided with a conical taper which is slightly divergent on the whole but provided with neither a cylindrical throat for a piston flow effect nor a venturi expanding portion.
In Japanese Patent Application Laid-Open No. 563/1972, a raw material is described to be injected into a point where a combustion gas stream has a sufficient mass velocity and in fact injected into a cylindrical throat (the smallest-diameter portion).
In Japanese Patent Application Laid-Open No. 183,364/1986, a material hydrocarbon oil is sprayed from a material hydrocarbon inlet tube passing through the side wall of the smallest-diameter portion of the venturi portion at an angle of 90.+-.20.degree. relative to the central axis.
In Japanese Patent Application Laid-Open No. 133,099/1977, a material hydrocarbon is introduced from one site relating to the central axis direction into the inlet portion of a cylindrical reaction chamber positioned downstream of a venturi expanding portion.
In U.S. Pat. No. 4,391,789, a material hydrocarbon is injected from a plurality of sites into a venturi reducing portion extending from a combustion chamber to a throat.
In U.S. Pat. No. 4,294,814, part of a material hydrocarbon oil is fed from the axial direction of a combustion chamber for the purpose of reducing the pressure loss of the reaction region, while when the fed material hydrocarbon oil passes together with a spirally flowing combustion gas through a venturi portion, the remaining material hydrocarbon oil is fed into the venturi expanding portion.
As described above, although provision of a material hydrocarbon inlet in a venturi reducing portion or a throat, is disclosed in known documents, no technical idea is found such that the particle size distribution or aggregate size distribution of a carbon black product is controlled as desired by providing a cylindrical throat having a piston flow effect, providing two or more material hydrocarbon spraying nozzles in the reactor axial direction from the throat to a venturi expanding portion and a reaction portion and spraying a material hydrocarbon oil through one or more selected material hydrocarbon spraying nozzles.
Japanese Patent Application Laid-Open No. 230677/1989 discloses a method wherein many and separately controlled carbon black material hydrocarbon oil streams are fed into respective reactor portions. Specifically, the oil streams are fed into an injection zone from a combustion chamber to a throat. In this portion, the combustion gas stream is not in a sufficiently piston-flowed state, so that the particle size distribution and the aggregate size distribution cannot be controlled as desired.
This invention is directed to the general art of preparing carbon black in an oil furnace process. In this generally known process, a suitable fuel, which is usually a hydrocarbonaceous gas or light liquid, is fed into a combustion chamber where it is substantially completely combusted with a suitable source of oxygen like air to form a hot combustion gas. This hot combustion gas, which contains substantially no material which is capable of further combustion, passes downstream into a reaction zone where the carbon black precursor is injected.
The carbon black precursor is suitably a hydrocarbon material, that is a petroleum oil. It is well known that this carbon black precursor hydrocarbon is usually a different hydrocarbon material than the fuel which is combusted to make the hot combustion gas. However, it is possible that the same hydrocarbonaceous materials could be used for both uses. The difference between these two materials, the fuel and the carbon black precursor, is that the fuel is substantially completely combusted to form the hot gas of gaseous combustion products, and the precursor is not combusted to any appreciable extent at all, but is only dehydrogenated to form substantially solid carbon black which is suspended in the hot combustion gas.
Thus, in this art, there is a recognized difference between the fuel which is used to form the hot combustion gas and the hydrocarbon material which is used to form the carbon black. The hydrocarbon material, which is used to form carbon black, is defined as having a CF value (defined as the cube root of the ratio of the boiling point of the hydrocarbon material in degrees Rankine to the specific gravity of the hydrocarbon material CF=3.sqroot.T.sub.B /S of less than 10.1, and a Bureau of Mines Correlation Index (BMCI) value of more than 100.
The heat in the hot combustion gas causes the hydrocarbon material carbon black precursor to be partially dehydrogenated into solid particles of carbon black in the reaction zone, and these particles are then separated from the stack gas and harvested. The stack gas is suitably passed pit of a flue.
As the term is used herein, "hydrocarbon material" is intended to refer to that hydrocarbon material which is the carbon black precursor. By contrast the hydrocarbon material which is used in the process of this invention as the fuel, it referred to as "fuel". While both materials may be hydrocarbonaceous in nature, and may be the same or different chemically, they perform very different functions and should not be confused with each other.
This process is generally carried out in an apparatus which is generally circular in cross section, but whose cross section diameter is varied at different points in the streamwise direction. It is reasonable to say that whether all of the portions of this apparatus are linearly aligned, or whether some of these portions extend at angles to each other, the process has a generally streamwise centerline, and therefore one can characterize different locations in this apparatus as having a different distance from this streamwise centerline. Of course, the apparatus may have a cross section which is not circular, e.g. elliptical, but this same concept of a streamwise general centerline still applies.
An object of the present invention is to provide a process and an apparatus for preparing a carbon black which enables the particle size distribution and the aggregate size distribution to be controlled as desired.